BGM-71 TOW
The BGM-71 TOW series, also known as the Close Combat Missile System-Heavy, are second-generation SACLOS (semi-active command line of sight) guided anti-tank missiles, and the United States' principle ground-based heavy infantry antitank system. TOW stands for "Tube-launched, Optically tracked, Wire-guided" in most variants: in the case of RF-guided versions, the W instead stands for "Wireless." History The fundamentals of the TOW system date back to US Army studies at Redstone Arsenal, Alabama beginning in January 1957. These were motivated by the failure of a manual command line of sight (MCLOS) missile system called DART, and IR SACLOS was under consideration as an alternative guidance method when DART was cancelled. TOW started development under the name heavy antitank weapon (HAW) with conceptual studies beginning 1958, intended to evaluate a missile system to replace the M40 recoilless rifle and the obsolete French-designed MCLOS anti-tank missiles in US service at the time (MGM-21A and MGM-32A ENTAC). The program quickly gravitated to the SACLOS research from Redstone and took on the name TOW, a description of the type of weapon they intended to develop. A feasibility demonstration of the guidance system was conducted before representatives of the various Ordnance boards in December 1960. Further feasibility studies in 1961 were just as positive, and 40 industrial firms were briefed in October 1961 to produce proposals for a functional system. From these, the proposals from Hughes Aircraft Company, Martin Marietta and McDonnell Aircraft Company were selected for further development, with parallel in-house development occurring at Redstone. The initial requirements issued in March 1962 were for a range not less than 2,000 meters, 90% first-round hit probability, 95% reliability, and a full system weight of no more than 200 pounds. The system would have to be capable of being launched from an infantry mount, armored or unarmored vehicle, or a helicopter. Three types of munitions were requested: an anti-tank round, a soft target round, and a chemical round (the latter two requirements were later dropped). In April 1962, the required range was increased to 3,000 meters. The first test-firings of all but the in-house launcher (which never produced a working system) took place in July 1962: none of these systems actually met the performance requirements, but it was concluded the Hughes offering was closest to the program's requirements and should be developed further. At the time the TOW was being directly evaluated against early versions of the MGM-51 Shillelagh missile for both the HAW role and another role, combat vehicle weapon system (CVWS) as there was significant overlap between the two requirements. In September 1962 Hughes was ordered to cease all design work on the gun-launched TOW they were developing for the CVWS role and focus on the tube-launched variant only. Hughes agreed, though stating that their tube-launched system could potentially fill the CVWS role anyway. The evaluations found that the TOW as it stood would be capable of defeating all heavy tanks likely to appear in the timeframe from 1965-1970, and the TOW development program was funded in the FY 1963 budget. Unguided test flights of a missile built to modified requirements first occurred in September 1963: the first test-firing was a spectacular failure, with the missile's launch motor exploding on ignition, and a later test in October 1963 resulted in a flight motor explosion. 32 guided tests occurring between Sepetmber 1963 and December 1964, with ten out first fourteen firings resulting in missiles failing to reach their target: of the remainder, the failure rate was 50%. Issues were revealed with almost all of the critical components of the system. Meanwhile, the first public display of a concept mockup of the system was at Redstone Arsenal in 1964. 62 further test firings of XBGM-71A missiles occurred between January 1965 and June 1966 with 17 failures and 33 hits in the tests that were not declared "no test," and the system continued to be plagued with reliability problems, resulting in initial production being deferred from 1967 to 1968. However, evaluations determined that all issues were technically possible to solve, and the program continued. It had, however, become increasingly clear that the weight goals (160 pounds for the launcher and 40 for the encased missile) were horribly over-optimistic: to avoid having to waste time redesigning both the weapon itself and the production process for a system the US Army urgently needed, the weight goals were suspended. In August 1967 US Combat Development Command, still unhappy with the reliability of the system, refused to type-classify the system: The Assistant Chief of Staff for Force Development did not approve the classification until April 1968, and deferred production to FY 1969 with delivery in January 1970 and full type-classification that July. TOW's xenon tail-lamp continued to cause problems during a sequence of 41 test firings in 1967, where 13 tests were failures, mostly because of the lamp or guidance wire breakages. However, by 1968 testing had shown more promising results, with helicopter tests of the XM-26 Armament Subsystem designed for the UH-1 Huey achieving direct hits in 92% of tests: a series of ground tests up to May 1969 showed a similar 90% reliability rate of missile prototypes after the prototypes internally referred to as Series 400, causing them to be nicknamed the "Golden 400." In 1969 the TOW program was again placed in direct competition with the MGM-51 Shillelagh: the House Armed Services Commission deleted the entire budget for the TOW program for FY 1970 in September 1969, stating that the missiles had almost identical capabilities but TOW was twice as expensive. However, the Army stated that in production the cost of the two systems would be comparable, and that the 3 year estimated delay to produce a portable version of the Shillelagh was unacceptable. TOW's budget was reinstated in November 1969 subject to a Senate Armed Services stipulation that both missiles would be competitively evaluated. This continued in debates around the FY 1971 budget, with the Army insisting that the only thing that should be discontinued was efforts to compare the two systems to each other. Ultimately the ground role went to TOW, while an evaluation of the two missiles in the air role found that TOW would actually be cheaper. Hughes delivered the first 25 production missiles in August 1969 and in a test of 33 missiles that December established a reliability rate of 90.6% with 28 out of 29 missiles scoring direct hits. US Army testing found a similar reliability rate of 90.8% with a hit probability of 80%. Further world was done to correct the system's sensitivity to vibration and moisture infiltration, and at this point the only part of the system not production ready was the requested optional night vision sight, battery charger, training set and vehicle mounting kits. The night sight was proving particularly troublesome and it was estimated it would not be ready until at least 1974. Distribution of production TOWs began in September 1970, and the first units in Europe were equipped by 13th November 1970, with training occurring thereafter at a rate of three battalions per month, with twenty-four battalions each equipped with six launchers by the end of the year. Each unit was then issued six more the following year. TOW saw its first use in combat in Vietnam in May 1972: this marked the first time that American soldiers had used an American-designed guided missile system in combat. The original night sight, an image intensifier, was terminated in 1973 with only twenty produced for testing with RVN units in 1972. This was both due to the disappointing performance of the prototype sight and the promising performance from the prototype AN/TAS-3 infrared night sight for the M47 Dragon. Plans to use this prototype sight were ultimately scrapped, and Texas Instruments began work on the TOW-dedicated AN/TAS-4 in 1973, with first deliveries occurring in November 1978 and issue to training bases commencing in September 1979. TOW is the world's most heavily exported anti-tank missile system, with some 36 countries employing it by the 1980s, increasing to 43 as of 2018. Design Details TOW is an IR-based SACLOS system in which a thermal tracking system on the launcher tracks an active IR beacon on the missile's tail, generating flight corrections to guide the missile to the point of aim and transmitting them by command wires in most variants. The infantry TOW launcher consists of a series of modules which allow a team of soldiers to carry it broken down: the main assemblies are the sighting unit, launch tube, traversing unit, tripod, and the fire control subsystem (FCS, also called the missile guidance set (MGS)) and silver-zinc battery power source (BPS). Older FCS modules have a space where a battery unit can be inserted into them if the BPS is not carried: the BPS grants a longer-lasting power supply and also includes a power conditioner to allow the missile to draw power from a vehicle's battery. The FCS connects to the launcher via a coil cable that is part of the traversing unit and is threaded through the bottom of the tripod: if a BPS is used, this connects to the FCS via its own cable. The infantry launcher is capable of 360 degree continuous traverse and 50 degrees of elevation. A variety of other mounting systems have been created for mounting TOW on various vehicles, including the hatch of a HMMWV light truck, a retracting pedestal mount for APCs, and various multi-shot box launchers for mounting on armored vehicles. Underwing mounts for helicopters are also available. The HMMWV mount uses the same components as the infantry version with the exception of the tripod, and TOW-equipped HMMWVs carry a standard infantry tripod to allow the launcher to be used dismounted from the vehicle if the tactical situation demands it. The missile in the TOW system is command-guided by the launcher: the missile's only function in the guidance system is to carry a thermal or IR beacon on its tail so that the launcher's IR tracker can determine its location and compare this to the current position of the crosshairs. All flight calculations are handled by the FCS module, then handed off to the missile's control surface actuators via either command wires or a one-way RF datalink in wireless variants. While all TOW systems use IR tracking as part of their guidance, the M151 and M220 launchers do not allow the operator to see the output from the integral IR system: the basic daysight tracker is an optical system. To improve functionality at night or in severe weather, a gunner IR sight was developed that clips on top of the daysight tracker and has its own eyepiece. The first model was the AN/TAS-4 which was first issued with the M151 launcher: later, the improved AN/TAS-4A was developed for the M220A2 launcher. These are gas-cooled IR sights requiring the use of pressurised gas bottles to cool them to operating temperature. The 1998 ITAS upgrade combined the IR and daysight systems into a single computerized sight module with a single common eyepiece that also featured an integrated laser rangefinding system with a range of up to 10 kilometers (6.2 miles). The ITAS IR scope is cooled by a modern SADA II electronic cryocooler, removing the need to carry single-use gas cartridges. ITAS also incorporated a new traversing unit that reworked the system's controls to be consolidated on a pair of handgrips instead of being a series of buttons and knobs scattered all over it as on previous versions. The TAS scope (AN/T55-12) weighs 54.5 lbs (24.7kg), is 26 inches (66cm) long including the eye cup, and 15.5 inches (39.4cm) in height and width. The TAS scope has the same SACLOS functionality as the previous versions, but also allows for a lock-on based engagement mode (almost an automatic command line of sight (ACLOS) firing mode) using tracking gates in a similar manner to FGM-148 Javelin's lock-on system: this is not fire-and-forget, but only requires the target to be kept within the sight's field of view, not centered in the crosshairs. ITAS also features a number of maintenance improvements including automatic boresighting without use of a separate collimator, and built-in training modes, with the system's laser designator also able to be used as part of MILES training. The TAS sight uses a different data connector to previous TOW launcher sights, a different mounting and requires controls that older traversing units do not have, and so cannot be mounted on the traversing unit of any previous TOW system. It is capable of being used with the older battery power source, but is issued with the newer lithium-ion battery box, along with a charger. It also uses a new fire control system, AN/TSW-15, as opposed to the older AN/TSQ-95 and AN-TSQ-102 respectively used by the M220A1 and A2 launchers. Firing procedure To load a TOW launcher, the shipping plug is removed from the missile tube's umbilical port, the front handling ring/cover is removed by releasing the metal band that secures it in place and pulling it off, and the tube inserted into the rear of the launcher's tube, locating it using the lugs at the front. The bridging clamp on the traversing unit is then closed and locked into place, establishing a connection between missile and launcher. The firing position for infantry TOW launchers is kneeling on the launcher's left side to use the weapon's sights, with the right arm reaching around under the missile tube to access the controls on the right side of the traversing unit. An arming safety lever is located on top of the bridging clamp and must be raised to the "arm" position to allow the missile to be fired: this is typically performed by a second crewman rather than the gunner. The trigger on the M151 and M220 launchers is located on the lower-right of the traversing unit just above one of the two control knobs for elevation and traverse. The trigger is equipped with a flip-up guard to prevent accidental firing. On the M41 launcher, the trigger is located on the front of the right hand grip. TOW requires a clearance of 9 inches (23cm) above and below immediately after launch to avoid damaging the control surfaces when they unfold, and a 30-inch (76cm) clearance between the line of sight and the ground is recommended at ranges from 500-900 meters (547-984 yards) to prevent terrain collisions. The TOW missile uses an internal thermal battery to provide it with power during its flight time: due to this needing to warm up and the internal gyroscope having to spin up, there is a 1.5 second delay between pulling the trigger and the missile firing. During this time several distinctive sounds are heard: on pulling the trigger a "pop" is heard immediately, this sound being an explosive bolt detonating to open the compressed nitrogen bottle that spins up the gyroscope. After this a sound rather like ticking can be heard, this being the sound of the thermal battery heating up: the whirr of the gyroscope may also be audible. TOW uses a soft-launch system with a small launch motor that burns for 0.05 seconds to eject the missile from the tube, burning out before it exits. The main engine only ignites when the missile's wings fully extend, this occurring about 7 meters (23 feet) from the launcher. The acceleration G-force from the flight motor firing is what arms the missile, typically about 0.53 seconds after launch when the missile is 65 meters (213 feet) from the launcher, making this the minimum effective range: this is intended to protect the operators in case of a launch motor failure. The flight motor burns out 1.6 seconds after launch, and the missile glides for the remainder of its flight time. The missile is first captured by the tracker about 1.85 seconds after launch: in wire-guided versions, if the tracker fails to detect the missile's thermal beacon at this point, the missile's command wires are automatically severed. When using the M151, M220 or the M41 in manual engagement mode, the operator must hold the sight's crosshairs over the target until impact: a visible light beacon is provided to help track the missile using the daysight, while the IR beacon the launcher itself uses is visible when using the IR night sight. It is important that the operator does not point the crosshair directly at the missile, as this will confuse the flight control software and the missile will veer off-course violently. When using the M41 in lock-on mode, it is only necessary to keep the target somewhere within the sight's field of view. Maximum flight time is about 20 seconds. In wire-guided versions, the system will automatically cut the command wires at the missile's designed maximum range. In RF guided variants, the RF transmitter shuts down as the missile reaches its maximum range. TOW's backblast danger zone is significant, extending 50 meters (55 yards) from the back of the launcher in a 90-degree arc: the "caution zone" is a further 25 meters (27 yards), and two further "caution zones" are located in the 45-degree arcs either side of the main 50 meter danger zone. After firing, the spent missile tube removed from the launcher. When time allows, the tube is destroyed in some expedient manner. Ammunition TOW missiles are issued packaged in a disposable fiberglass and epoxy protective launch tube with alignment lugs at the front end, an umbilical data connector on the top covered with a protective plastic cap in transit, and a moisture infiltration indicator in the middle of the rear bursting disc. The missile sections, from front to back, are the warhead (and any standoff probe the missile has), flight control electronics, flight motor (which fires through diagonal vents angled at 30 degrees in the missile's midsection), folding wings, gyro and battery section, launch motor with the wire dispensers or RF receivers mounted alongside it, control surfaces, and finally the launch motor exhaust and visual and IR beacons on the rear surface. In TOW-2A and B the missile electronics are relocated to the rear section of the missile due to the extended warhead. All TOWs except 2B use a crush detonator either in the missile's nose, or on the standoff rod if present. Wired versions of the missile uses twin command wires, each of which consists of two copper signal transmission wires and one steel wire to prevent the copper wires from breaking. The command wires are coated in a thin layer of varnish for insulation, though the effect is minimal as the coating must be thin enough for the wires to flex freely. The wires are anchored to the inside of the launch tube, with the wire spools inside the missile itself. As the missile flies, the command wire unspools out the back, guided by the dispensers: it is not under tension, and simply trails along the ground. Due to this, it is dangerous to fire wired TOW variants over live electrical lines: if this occurs it can destroy the launcher's electronics. In addition, TOW's effective range reduces drastically if it is fired over water, due to the conductivity of the water interfering with the command signals. The command wire is stored wrapped around the launch motor assembly in multiple layers: in this way even the original TOW could contain 6.5 kilometers (4 miles) of command wire (while the missile automatically cut its wires at 3,000m, the original wires were actually 3,250m long). Missile tubes have a 20-year shelf life and require no maintenance other than routine checks on their moisture indicators. Ammunition variants BGM-71A 1970: "Basic TOW," first production model, range of 3,000m. Single-stage HEAT warhead. No longer produced. BGM-71B Also referred to as BGM-71A-1. Basic TOW variant with improved booster and extended control wires, giving a range of 3,750m. No longer produced. BGM-71C 1978: "ITOW," improved TOW with a collapsible standoff probe for better shaped-charge performance, but still a single-stage warhead. No longer produced. BGM-71D 1983: "TOW-2," generally improved BGM-71C variant with guidance and flight motor improvements and an enlarged, full-caliber warhead. Changed tracking flare to emit pulses rather than a steady light to prevent the tracker being jammed by the Soviet Shtora-1 active protection system. No longer produced BGM-71E 1987: "TOW-2A," tandem charge version optimized to defeat reactive armor, with a precusor warhead mounted on a long standoff probe on the missile's nose. Thermal tracking beacon changed to a xenon lamp, rendering the system completely immune to Shtora. Also used variable beacon flash frequencies to allow TOW launchers to identify their own missiles: prior to this, TOW launchers could not be fired at ranges closer than 300 meters (330 yards) due to the possibility of a tracker acquiring another launcher's missile. BGM-71F 1987: "TOW-2B," overfly top-attack (OTA) variant using two downward-firing tantalum explosively formed penetrators, conceptually based on the 1985 Swedish RBS 56 BILL anti-tank missile. The two penetrators are fired at slightly offset angles to increase the probability of a hit. Uses a different flight profile to other TOW variants, flying 2.25 meters above the tracker's line of sight, and a dual-mode laser/magnetic detonation sensor similar to the later FGM-172 SRAW to detect targets. The new warhead section was designed by Aerojet, with the triggering system by Thales Missile Electronics. Same improved Xenon beacon as 2A. TOW 2B Aero 2002: Sub-variant of the BGM-71F, using an aerodynamic nose cap that increase range to 4,500m (2.8 miles) and longer command wires. Gen2 version has enhancements to defeat active protection systems. BGM-71G F variant with a different top-attack warhead, never produced. BGM-71H "TOW-BB." BGM-71E modification with a bunker-busting warhead. Same enhanced range as TOW 2B Aero. TOW-RF Denotes a radio-frequency (RF) guided TOW. The RF transmitter is contained inside the launch tube and requires no modification to the launcher, using the standard FCS and umbilical data connector. The missile itself is an E, F, 2B Aero or H variant. TOW-2N Original wireless TOW concept, cancelled in 1989. TOW-FF Fire-and-forget TOW with an imaging infrared focal plane array similar to the FGM-148 Javelin. Began work in 2000, cancelled by the US Army in 2002. BTM-71 Training version of the TOW, denotes a missile with a live booster but a dummy warhead. STD BTM-71A1, TOW 2 BTM-71D-1B, TOW 2A BTM-71D-1B and TOW 2B BTM-71E-3B are practice rounds corresponding to Basic TOW, TOW-2, TOW-2A and TOW-2B. System variants M151 Basic TOW launcher. Original production only had a daysight tracker. M220A1 Improved M151, designed for use with legacy missiles and not fully able to take advantage of the features of TOW models after C. Used AN/TAS-4 night sight. M220A2 Improved TOW launcher designed alongside TOW-2 in the 1980s. New digital FCS, used AN/TAS-4A night sight. M220A4 Marine Corps HMMWV TOW launcher, unclear improvements. Bradley TOW Twin-tube launcher developed for the M2 Bradley IFV. M65 Four-tube hardpoint-mounted launcher designed for helicopters. TOW LWL Lightweight launcher. Spanish TOW launcher variant, currently uses a combined sighting unit similar to the ITAS designed in 1995. M41 ITAS Improved target acquisition system. 1998 redesign of the launcher with a combined sighting system, improved FCS, and improved lithium-ion power source (LPS). 709 systems were procured by the US Army from 1999-2003, and production restarted in April 2005. M41 ITAS-FTL ITAS-FTL adds integration with the Far Target Location system with a device called PADS (position attitude determination subsystem) that mounts on top of the ITAS scope. This gives precise GPS coordinate data using differential tracking, and allows the ITAS system's laser rangefinder/designator to be used to designate targets for other weapons. The most current version is M41A7, which incorporates new image processing technology in the ITAS sight to provide automatic image stabilization and focus and contrast adjustment. IBAS Improved Bradley acquisition subsystem, equivalent of the ITAS upgrade for Bradley TOW launchers. Toophan Toophan (Persian توفان "Storm") is an Iranian clone of TOW, starting out as a straight copy mainly recognizable by the shorter legs of its tripod, before becoming a unique system with capabilities not present on the original TOW. Newer versions use semi-active laser homing (SALH) instead of IR SACLOS. Ammunition-wise, Toophan-1 is analogous to Basic TOW, Toophan-2 to ITOW with the 2M variant more comparable to TOW-2A, Toophan-3 to TOW-2B, Toophan-4 a unique thermobaric warhead, Toophan-5 the first laser-guided variant, Toophan-6 a bunker-busting thermobaric warhead, and Toophan-7 an unknown system currently under development. Qaem Qaem (Persian قائم "right") is a 2010 SALH Toophan variant designed specifically to target helicopters, with an added secondary flight motor for improved performance. The follow-on Qaem-M adds a proximity fuze. References * TM 9-1425-470-12 "Operator's and Organizational Maintenance Manual for TOW Heavy Antitank/Assault Weapon System," Headquarters, Department of the Army, January 1974 * TM 9-1425-472-12 "Operator's and Organizational Maintenance Manual for TOW Weapon System Guided Missile System M220A1," Headquarters, Department of the Army, January 1980 * FM 23-34 "TOW Weapons Systems," Headquarters, Department of the Army, 17 August 1994 * FM 3-22.32 "Improved Target Acquisition System, M41," Headquarters, Department of the Army, July 2005 * "History of the TOW Missile System," Army Aviation and Missile Command (Redstone Arsenal, Alabama), Mary T Cagle, 20 October 1977 Category:Anti-tank missiles Category:Missile launchers